X-ray or gamma ray systems or devices – Specific application – Diffraction – reflection – or scattering analysis
Reexamination Certificate
1999-03-10
2001-02-27
Bruce, David V. (Department: 2876)
X-ray or gamma ray systems or devices
Specific application
Diffraction, reflection, or scattering analysis
C378S057000, C250S363030, C356S310000
Reexamination Certificate
active
06195412
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the field of energy beam imaging, and in particular, to a method and apparatus for x-ray imaging sub-volumes by sequentially filtering and focusing individual source points with a confocal coded aperture.
2. Description of Related Art
The ability to non-destructively analyze microscopic volumes within large objects, for example multi-layer microelectronic packages, requires use of penetrating radiations such as X-rays. Current techniques for inspecting these volumes typically employ transmission radiography, which is similar to medical X-ray imaging. Computed tomography (CT) can be used to view individual planes of interest in such packages. The resolution of these systems is limited by the x-ray source, that is, the system resolution defined by the spot size of the X-ray source. Transmission methods suffer from an inability to differentiate three-dimensional information. In other words, a p three-dimensional space must be mapped onto a two-dimensional plane. Moreover, techniques such as CT require that the whole object be inspected, which can unnecessarily generate large quantities of data and require computationally intensive and time-consuming reconstruction processes to mitigate CT image artifacts.
Coded aperture imaging systems were historically developed to image points of non-focusable radiation from sources such as x-ray or gamma stars, and discrete, localized nuclear events. The literature describes many attempts to use coded apertures to image extended two-dimensional and three-dimensional objects, but the results have never exceeded the type of resolution and detail achievable through other means, such as transmission or computed tomographic (CT) radiography. This limitation on resolution and detail is primarily due to the coded aperture impulse or frequency response and the response of the system to out-of-plane sources of scattered radiation. Since all previous systems attempt to image the entire object instantaneously, the degrading effects of the aperture quickly become dominant as the size of the object increases.
The technology associated with coded aperture imaging has been around since the late 1970's. The earliest work in the field, using coded aperture arrays, is described in “Coded Aperture Imaging with Uniformly Redundant Arrays”, E. E. Fenimore, and T. M. Cannon, Feb. 1, 1978,
Applied Optics
, Vol. 17, No. 3, pp. 7-347.
Coded aperture imaging using neutron sources during the early 1990's is described in “Three-Dimensional Information from Real-Time Encoded Images”, K. W. Tobin, J. S. Brenizer, and J. N. Mait,
Optical Engineering
, Vol. 29, No. 1, January, 1990.
The nature and characteristics of Fresnel zone plate (FZP) X-ray source focusing technology is described in “Design and Fabrication of Fresnel Zone Plates with Large Number of Zones”, Z. Chen, Vladimirsky, M. Brown, Q. Leonard, O. Vladimirsky, F. Moore, F. Cerrina, B. Lai, W. Yuri, and E. Gluskin, J. Vac.,
Sci. Technology
, B 15(6), November/December 1997, p. 2522.
An x-ray spectrometer is described in U.S. Pat. No. 5,757,005—Callas, et al. that provides images of an x-ray source. Coded aperture imaging techniques are used to provide high resolution images. Imaging position-sensitive x-ray sensors with good energy resolution are utilized to provide what is described as excellent spectroscopic performance. The system produces high resolution spectral images of the x-ray source which can be viewed in any one of a number of specific energy bands.
A system utilizing uniformly redundant arrays to image non-focusable radiation is disclosed in U.S. Pat. No. 4,209,780—Fenimore, et al. A uniformly redundant array is used in conjunction with a balanced correlation technique to provide a system said to have no artifacts, such that virtually limitless signal-to-noise ratio is obtained with high transmission characteristics. Additionally, the array is formed as a mosaic to reduce required detector size over conventional array detectors.
Many other patents and publications reference coded aperture imaging techniques but they are all based on imaging a single, localized source of scattered energy, such as celestial sources, or instantaneously imaging a distributed source of energy from an extended body. There are no other known techniques that utilize the inventive arrangements taught herein.
Accordingly, there is a need for a new method and apparatus for imaging three-dimensional objects, particularly for imaging small volumes of interest within a larger volume or object, using non-focusable radiation.
SUMMARY OF THE INVENTION
The need for a new method and apparatus for imaging three-dimensional objects, particularly for imaging small volumes of interest within a larger volume or object, using non-focusable radiation, is satisfied by a method and apparatus which utilizes a confocal coded aperture to image three dimensional objects. The complimentary steps of imaging one primary point of focused X-ray energy, and by shielding or baffling the detector system to reduce the collection of stray sources of scattered energy, make possible high resolution, high-speed data collection and image displays.
Confocal coded aperture (CCA) imaging is a new method for imaging small volumes of interest within a larger volume or object using non-focusable radiation. The technique depends on the availability of a small, highly focused spot of X-ray energy generated by a Fresnel zone plate (FZP) or similar diffractive optic. The focal point of the highly focused spot of X-ray beam is scattered from the internal structure of a target inspection volume. The reconstruction of the point of the scattered X-ray beam is accomplished using a highly efficient coded aperture. As the spot is scanned through the volume of interest, a reconstruction and visualization of the structure and material characteristics is non-destructively achieved. The method overcomes limitations usually observed with image reconstructions based on coded apertures by filtering and focusing one source point at a time.
The CCA system taught herein makes use of a new technique for focusing the x-ray source that can achieve a very high resolution spot, for example on the order of less than 0.5 microns. The focused x-ray spot is scanned through a small volume of interest within the object. The scattered spot at a given coordinate is reconstructed using a highly efficient, non-diffractive collection aperture known as a coded aperture. The coded aperture is uniquely configured with a shielding baffle to mitigate collection of scattered energy from other coordinates within the volume. A digital correlation reconstruction algorithm is used to further focus and reconstruct the energy scattered from the point of interest in the target volume. As the x-ray spot is scanned through a three-dimensional sub-volume of the object, a high-resolution image is obtained representing both the structural and material characteristics of the object. This information is suitable, for example, for the non-destructive detection and analysis of the various manufacturing anomalies that can occur in complex, three-dimensional objects.
A method for imaging a target volume, in accordance with the inventive arrangements, comprises the steps of: radiating a small bandwidth of energy toward the target volume; focusing the small bandwidth of energy into a beam; moving the target volume through a plurality of positions within the focused beam; collecting a beam of energy scattered from the target volume with a non-diffractive confocal coded aperture; generating a shadow image of the aperture from every point source of radiation in the target volume; and, reconstructing the shadow image into a 3-dimensional image of the every point source by mathematically correlating the shadow image with a version of the coded aperture.
The method can further comprise the step of correlating the shadow image with a digital or analog version of the coded aperture.
The method can comprise the step of generating the shadow image o
Thomas, Jr. Clarence E.
Tobin, Jr. Kenneth William
Akerman Senterfitt & Eidson, P.A.
Bruce David V.
Dunn Drew A.
UT-Battelle LLC
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